īˈsidēəm noun
( plural isid·ia -ēə)
Etymology: New Latin, from Isidium, supposed genus of lichens, irregular from Isis genus of gorgonians + Greek eidos form; from the resemblance of lichens that have isidia to gorgonians — more at idol
: an outgrowth from the surface of the thallus in certain lichens that resembles a soredium